Stick it in the washing machine if it is a nylon collar. If it's leather, it would be like killing it. Since water is bad for leather so I wouldn't dump it into water. I washed my nylon collars while I wear them when I shower, after that I take it off and there, it's clean, unless you want to clean it more by adding detergent. For leather collars, use leather conditioner or use a damp cloth wipe it. I haven't cleaned my leather one since I got it.